A September blog post written by AP Stylebook editors explains the change:

Scientists who consider themselves real skeptics – who debunk mysticism, ESP and other pseudoscience, such as those who are part of the Center for
Skeptical Inquiry – complain that non-scientists who reject mainstream climate science have usurped the phrase skeptic. They say they aren’t skeptics
because “proper skepticism promotes scientific inquiry, critical investigation and the use of reason in examining controversial and extraordinary claims.”
That group prefers the phrase “climate change deniers” for those who reject accepted global warming data and theory. But those who reject climate science
say the phrase denier has the pejorative ring of Holocaust denier so The Associated Press prefers climate change doubter or someone who rejects mainstream
science.